For a conventional liquid crystal display device, its backlight source mainly includes a back plate, a reflecting sheet and a light guide plate. In order to provide the backlight source having a weight within a predetermined range, usually the back plate is made of a lightweight aluminum alloy material, but it may easily be deformed when the back plate is engaged with a sealant. Along with the development of a flat-panel computer with a super narrow bezel, the backlight source also needs to be provided with a super narrow bezel, i.e., a wall thickness of the sealant needs to be smaller than 0.65 mm. At this time, it is difficult to shape the sealant, and the sealant may easily be deformed during the assembling. In addition, an adhesive tape for the fixation of a liquid crystal cell is too narrow to cover a gap between the sealant and the light guide plate, so it is difficult to prevent the occurrence of such a phenomenon as bright lines for the backlight source.